In general, a portable terminal provided with radio communication function, obtains HTML file, image file, sound file or other contents on a content server according to the following procedures.
First, the portable terminal transmits a content acquisition demand specifying the URI (Universal Resource Identifier) to the gateway server by radio communication, The gateway server obtains the specified content from the content server specified in the URI. Here, the gateway server and the content server are network connected by Internet or the like. The gateway server that has obtained the content, transmits the content to the portable terminal. Upon the reception of content, the portable terminal display this content using an information display on the portable terminal. The content sometimes includes a plurality of URI format link information to the other contents, and if the user operation selects on of them, the selected content is obtained again.
Here, both the communication from the portable terminal to the gateway server and the communication from the gateway server to the content server are low in communication amount; therefore, most of time required for content acquisition is occupied by the transmission time of content from the content server to the gateway server and the transmission time of content by radio communication from the gateway server to the terminal.
On the other hand, as for a general client terminal which is not a portable terminal, as a technology for reducing the time from the content acquisition demand emitted by the user to the actual display of that content on the client terminal, there is a technology to prefetch previously contents that can be asked by the client to obtain. This technology is classified roughly into a first method for storing in the portable terminal and a second method for storing in the gateway server (or proxy server).
As an example of the prefetch technology of the first method, the Japan Patent Publication HEI 6-110926 proposes a technology for investigating link information in the content displayed actually on the portable terminal, and prefetching by the portable terminal the content on the content server contained in the link information before the link is specified by the user, and holding in the portable terminal. When a next content is demanded to be obtained by the user operation, a rapid response is realized by displaying the demanded content, if it exists in a group of prefetched contents in the terminal. On the other hand, the Japan Patent Publication HEI 8-87526 proposes a technology for reducing the necessary memory on the terminal side compared to prefetch the whole contents, by giving priority order based on the user operation history or the like on the client terminal side or the server side, when the terminal prefetch the content, and prefetching only those of high priority and holding on the terminal side.
As an example of the prefetch technology of the second method, the Japan Patent Publication HEI 11-149405 proposes a technology for prefetching the content referred to by the content asked by the terminal to obtain and caching in the server side. Moreover, a technique to reduce the content to prefetch by giving priority to each cached content according to its request frequency, and prefetching based on the priority of the content asked by the user to obtain or the importance of that user. For instance, if the priority of the content asked by the user to obtain if “high”, the whole contents referred to by this content are prefetched or reloaded, and if the priority is “middle”, only already cached content among contents referred to by this content is reloaded, and it the priority is “low”, only content already cached and having “high” priority among contents referred to by this content is reloaded. Here, “reload” means the processing of replacing already cached content with the newest original content on the content server, and “prefetch” means the processing of obtaining non cached content from the content server and caching the same.